Production of hot mix cold laid bituminous pavements



Patented Jan. 4, 1933 PRODUCTION OF HOT MIX COLD LAID BI- TUMINOUS PAVEMENTS Charles M. Baskin, Toronto, Ontario, Canada, as-

signor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application August 30, 1934, Serial No. 742,147

3 Claims.

This invention relates to improvements in the manufacture of bituminous pavements, and refers particularly to a method that eliminates the necessity of large stationary plants and the use of excessive temperatures. This method is also designed to use damp or moist mineral matter without preheating to high temperatures to completely eliminate the water.

In carrying out the invention, low viscosity oils are used. as primers for the mineral aggregate and hard brittle asphalt in powder form is used as a thickener. Low viscosity oils derived from cracking operations are preferred as these have greater solvent power for hard brittle asphalts. The solvent power of the priming oil is important insofar as greater speed of amalgamation or solution of hard brittle asphalt powder in the priming oil is obtained.

By the use of low viscosity oils all kinds of mineral aggregates are thoroughly coated without having to preheat the priming oil. Mineral aggregates for road construction vary with location and economic conditions. The variation is principally in what is known as graduation, or quantities of the different size particles in the total mass. It is evident that the greater the quantity of fine particles in the total mass, the greater is the surface area, in which case the priming oil has to be of very thin consistency so that it will effectively cover such large surface areas. If high viscosity oil primers are used, it requires preheating of the priming oils as well .as very often necessitating preheating of mineral aggregates. In this case it is preferred to use oils from cracking operations, ranging in Furol viscosity at 122 F. all the way from seconds to 250 seconds.

The method consists of introducing the powdered asphalt, having a softening point above 240 F., and the priming oil into the mineral aggregate at one and the same time. As soon as these materials are introduced and the whole mass is partially mixed, heat is applied directly into the mixer or on the mass of mineral matter primer and powdered asphalt while in the process of mixing. Heat applications can be either by means of a direct flame, such as an oil burner, or by means of hot gases from engine exhaust, etc. The mixture thus obtained can then be laid as a pavement and further amalgamated by means of rollers and traffic.

The function of introducing heat into the mixture while in the process of mixing is two-fold:

First-To raise the temperature of the mass to a point where the bituminous materials properly distribute themselves over the mineral particle surfaces in spite of the moisture present on the surfaces. It is found that in order to effectively coat wet mineral aggregate with fluid bitumens (fluid at atmospheric temperature), it is not necessary to dry the mineral matter, but merely to preheat it to approximately F. The application of direct heat does not affect the asphalt binder. This has been demonstrated in such tests as reduction of slow curing liquid asphalts to 50 penetration at 77 F., by setting fire to the liquid asphalt. Only the volatile fractions that come out of the mass of asphalt in powder form burn, while the residue remains entirely intact and is very much the same as if this reduction to 50 penetration had been made by direct distillation. Furthermore, in this case the application of heat is not suiiicient to raise the temperature of the bituminous materials to the burning point, which, even in case of light oil primers, is over 300 F.

Second.Applying a slight amount of heat directly into the mixture gives an initial start to amalgamation and raises the consistency of the mixture to a point where further amalgamation is not affected by either water or temperature change.

Resistance to water action of paving mixtures is mainly dependent on the consistency of the asphalt films. By the introduction of a little heat directly into the mixture, it is insured that the consistency of the asphalt films on the mineral particle surfaces is at least as high as 50 F. softening point, which is a consistency that will withstand the action of water. This partly amalgamated mixture may be laid hot or allowed to cool or partially cool before laying. Also, giving the mixture a start by slight preheating insures the continuation of amalgamation under further compression by roller and traflic.

The foregoing description is merely illustrative and various changes and alternative arrangements may be made within the scope of the appended claims in which it is my intention to claim all inherent novelty in the invention as broadly as the prior art permits.

I claim;

1. A method of producing a paving mixture which comprises heating a wet mineral aggregate of 150 F., mixing the heated aggregate with a low viscosity priming oil and powdered hard asphalt, and heating the mixture by contacting with a flame while mixing to partially amalgamate and to' raise the softening point of the bituminous portion of the mixture to at least 50 F.

2. A method of producing a paving mixture which comprises heating a wet mineral aggregate to 150 F., mixing the heated aggregate with a priming oil having a Furol viscosity of from 60 seconds to 250 seconds at 122 F. and powdered hard asphalt, and heating the mixture by contacting with a flame while mixing to partially amalgamate and to raise the softening point of the bituminous portion of the mixture to at least 50 F.

3. A method of producing a paving mixture which comprises heating a wet mineral aggregate to' 150 F., mixing the heated aggregate with a low viscosity priming oil and powdered asphalt having a softening point above 240 F. and heating the mixture by contacting with a flame while mixing to partially amalgamate and. to raise the softening point of the bituminous portion of the mixture to at least 50 F.

CHARLES M. BASKIN. 

